1. Field of the Invention
The present invention relates to a zoom lens system, and more particularly to a compact zoom lens system having a high variable magnification ratio and a high resolution.
2. Description of the Prior Art
In order to effect downsizing and to improve the image quality and function of video cameras, downsizing of high performance and high function zoom lenses and image pick up devices is required. Consequently, a high zoom ratio obtained by reducing the wide angle focal length of the system and extending the telescopic focal length of the system, and a high image quality, attained by compensating aberrations, are necessitated. On the other hand, a lens system manufactured at low cost while maintaining high performance is called for in order to maintain economic competitiveness. Consequently, a zoom lens capable of providing a wide view angle, a high zoom ratio, and a high resolution with a smaller F number of lenses is needed.
A conventional zoom lens disclosed in U.S. Pat. No. 5,185,678 comprises five lens units of positive, negative, positive, positive, and negative refractive powers in sequence from the object side to the image side. Each lens unit comprises a single lens element or cemented lens. The total number of lens elements of the conventional zoom lens is about 16 to 20. Another conventional zoom lens is disclosed in U.S. Pat. No. 6,061,186, also comprising five lens units of positive, negative, positive, positive, and negative refractive powers. The number of lens elements of the conventional zoom lens is about 17 to 19. It is clear that number of lens elements of above-mentioned conventional lens units is relatively large, the total length of the lens system is great, and the production cost is high.
Hence, it is desired to have a zoom lens that overcomes the above-mentioned drawbacks.